The disclosure generally relates to light emitting semiconductor devices and systems. It particularly relates to systems used for IR inspection and imaging of single and bonded semiconductor substrates, MEMS (MicroElectro-Mechanical Systems) and MEMS-type constructions and bio-sensors.
A semiconductor light source, such as a light emitting diode, source with a peak wavelength operating in the 1.0 to 1.1 μm band is very useful for certain known and future applications. For example, the wavelength may be used for MEMs inspection or the ability to see through semiconductor wafers. The wavelength may be detected by certain detection means, such as standard hi-resolution CCD (charge-coupled device) arrays. The wavelength also has medical applications, for example, blood analysis of diabetics.
Current illuminators and literature in this area refer to laser diode sources for these applications. These are not ideal for this type of application as laser speckle, scatter and lack of uniformity cause difficulties for inspection type applications.
Current implementations use a strained InGaAs quantum well surrounded by GaAs cladding layers and have been well documented in the peer reviewed journals and in some patents. All references focus on the use of these structures for laser diode and not other semiconductor light sources, such as light emitting diode (LEDs) type illuminators, and certainly not in arrays of LEDs. Manufacture of arrays of laser diodes is not practical, making LEDs a more attractive implementation in which to achieve the desired wavelengths. However, as mentioned above attaining the desired wavelengths in a structure that can be manufactured in arrays creates some difficulties.
Another difficulty with the current designs arises in trying to extend the wavelength of the peak emission wavelength beyond 1 μm. To achieve this, the indium content of the InGaAs strained quantum well has to be increased and the quantum well thickness also increased. The thickness approaches the critical thickness for the quantum well. Thicknesses larger than the critical thickness causes defects in the layers, in turn leading to a relaxation of the lattice that may result in device failure and poor performance.